Abstract

The present study aims to investigate the protective effect of bees’ honey against metanil-yellow-induced hepatotoxicity in rats. Rats were divided into 7 groups: control group; three groups treated with 50, 100, and 200 mg/kg metanil yellow, and three groups treated with metanil yellow plus bees’ honey for 8 weeks. The obtained data showed that the antioxidant/anti-inflammatory activity of bees’ honey reduced the oxidative stress in the liver tissue and downregulated the inflammatory markers. In addition, the elevated levels of AGE and the activated NF-κB in the metanil-yellow-treated animals were significantly attenuated. Moreover, the levels of TNF-α and IL-1β were significantly attenuated as a result of bees’ honey administration. Furthermore, the histopathological examination of the liver showed that bees’ honey reduced fatty degeneration, cytoplasmic vacuolization, and necrosis in metanil-yellow-treated rats. In conclusion, the obtained data suggest that bees’ honey has hepatoprotective effect on acute liver injuries induced by metanil-yellow in vivo, and the results suggested that the effect of bees’ honey against metanil yellow-induced liver damage is related to its antioxidant/anti-inflammatory properties which attenuate the activation of NF-κB and its controlled genes like TNF-α and IL-1β.

1. Introduction

Metanil yellow is a highly-water-soluble dye. It belongs to the mono azo group of the dyes. Although the use of metanil yellow as a colorant agent is not permitted, it is still widely used as a colorant in many food industries. It is extensively used in the developing countries as a colorant in sweet meat, ice-creams, soft drinks, and beverages [1]. Because of its orange-yellow color, metanil yellow is also widely used in the coating of turmeric. It is extensively used in paper, leather, and many textile industries as a dye and colorant for the wool [1, 2]. Moreover, it is also used as a colorant for lacquers and cosmetic products. Furthermore, the dye is highly suitable for the preparation of colored water-fast inks [3] and can also be used analytically for the determination of trace amounts of Mo (VI) [4].

Like all azo dyes, the toxicity data showed that intraperitoneal and intratesticular administration or the oral feeding of metanil yellow in the laboratory animals like rats and guinea pig produces testicular lesions because of the damage of the seminiferous tubules and the decreased rate of spermatogenesis. Metanil yellow also results in alteration of the rat haematopoietic system and reduction of mucin secretion of the rat’s intestinal cells [5]. In the case of oral administration, metanil yellow causes toxic methaemoglobinaemia [6] and cyanosis [7] in humans, while allergic dermatitis results from its direct contact with the skin [8]. In addition, metanil yellow has tumor-inducing effects and can also create intestinal [9] and enzymatic [10] disorders in the human body. Metanil yellow is not mutagenic but it can alter the expression of many genes [1].

The major metabolic pathway for detoxification of azo compounds proceeds via the reduction of the azo linkage leading to the formation of aromatic amines [1]. Reduction of azo compounds is catalyzed by liver microsomes [11], cytosolic enzymes, and colonic bacteria [12]. Reduction products of some azo compounds are found to possess toxic and mutagenic properties [13]. The two metabolites of metanil yellow are p-aminodiphenylamine and metanillic acid, which are found to be toxic in rat gut mucosal epithelium [14].

Honey is a highly healthy material. Bees’ honey is considered to be a balanced food source [15]. Although bees’ honey is considered as a natural product, its chemical composition is very complex. Bees’ honey contains about 180 compounds. The main constituents include enzymes, vitamins, amino acids, and minerals [16]. Previous studies showed that bees’ honey was widely used in the folk medicine [17]. Cumulative data showed that bees’ honey possesses a considerable anti-inflammatory, antioxidative, and antitumor activity. In addition, it is considered a potent radical scavenger especially for hydroxyl radicals. Moreover, it prevents the depletion of the antioxidant enzymes. Furthermore, it plays a key role in both normalizing of the kidney functions and protection of the liver from different toxic agents [15–17].

The present study aims to evaluate the hepatotoxic effects of metanil yellow as well as the hepatoprotective effects of bees’ honey on rat liver. In addition, this study aims to investigate a possible pathway for the protective effect of bees’ honey.

2. Materials and Methods

2.1. Animals

Adult male albino rats weighing 190–210 g were used in the present study. Animals were maintained under normal conditions and fed a normal diet with free access to water ad libitum. Rats were randomly divided into 7 groups, 10 rats each, as follows.Group 1: this group of animals was healthy normal rats and serves as untreated control group.Groups 2–4: animals of these groups were orally given metanil yellow at a dose of 50, 100, and 200 mg/kg body weight (lower than 1/20 of LD50) [9]. Groups 5–7: animals of these groups were orally given Metanil yellow at a dose of 50, 100, and 200 mg/kg body weight (as in group 2–4) in addition to bees’ honey 2.5 mg/kg body weight daily [17] for 8 weeks.

At the end of the experimental duration, the animals were weighed, anesthetized, and sacrificed. The liver was removed and washed with cold normal saline and divided into parts. The first part was used to prepare the liver homogenate, the second was used to prepare the nuclear extract for electrophoretic mobility shift assay (EMSA), and the third part was used for histopathological examinations.

2.2. Blood Collection for Estimation of Liver Functions

Before sacrificing the animals, blood was collected from retro-orbital plexus. The blood was incubated at 37°C for 10 min and centrifuged at 5,000 g for 10 min. The resulting serum was used for analysis of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total protein (t. protein), albumin, total bilirubin, gamma glutamyl transferase (GGT), and serum lactate dehydrogenase (LDH).

The levels of ALT, AST, ALP, t. protein, albumin, t. bilirubin, and GGT in the serum of all rats were determined by using the commercially available kits. The required kits were purchased from BioSystem (Barcelona, Spain). All analyses were performed according to the instructions of the manufacturer.

2.4. Determination of LDH

LDH was determined according to the method of King [18]. 100 μL of serum was added to 1.0 mL of buffered substrate (sodium pyruvate 37.5 mM in phosphate buffer 100 mM, pH 7.4). The mixture was incubated at 37°C for 15 minutes. After adding 200 μL of NAD+ solution (10 mg/mL in phosphate buffer), the incubation was continued for further 15 minutes. The reaction was stopped by adding 100 μL of 2,4-dinitrophenylhydrazine (0.02% in concentrated HCl). The tubes were incubated again at 37°C for 15 min, then 7.0 mL of 0.4N NaOH was added, and the developed colour was measured using a spectrophotometer using phosphate buffer as blank.

2.5. Liver Homogenate Preparation

The liver of different groups was dissected and rinsed thoroughly with ice-cold normal saline. Moreover, it was smashed in a homogenization buffer containing a protease inhibitor tablet [19, 20]. The solution was sonicated in an ice bath for 30 sec followed by centrifugation at 13000 rpm for 4 min at 4°C. The supernatant was stored at −80°C and assayed for protein concentration using BCA kit (Pierce, Rockford, IL, USA) according to the instruction of the manufacturer [21]. Bovine serum albumin was used as a standard.

The liver homogenate was used for the determination of the level of lipid peroxidation (MDA), the concentration reduced glutathione (GSH), and the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-px), glutathione-S-transferase (GST), and catalase. In addition the levels of advanced glycation end products (AGE), nitric oxide (NO), interleukin 1 beta (IL-1β), and tumor necrosis factor alpha (TNF-α) were assayed in the liver homogenate. The second part of the liver from each group was stored in 10% neutral formalin solution and used for histopathological examinations.

2.6. Assay of the Oxidant/Antioxidant Markers of Liver Homogenate

2.6.1. Reduced GSH

Reduced GSH was measured by colorimetric end point assay using dithionitrobenzoic acid method described by Sayed [22]. GSH concentration was expressed as nmol/mg protein using GSH standard calibration curve.

2.6.2. Determination of GSH-Px Activity

The activity of GSH-Px in the liver homogenate was measured by the method of Paglia and Valentine [23] with slight modification. The oxidation of NADPH to NADP+ is accompanied by a decrease in absorbance at 340 nm (A340) providing a spectrophotometric means for monitoring GSH-px activity. The molar extinction coefficient for NADPH is 6220 M−1 cm−1 at 340 nm. To assay GSH-px, the tissue homogenate was added to a solution containing glutathione, glutathione reductase, and NADPH. The enzyme reaction was initiated by adding the substrate, hydrogen peroxide, and the absorbance at 340 nm (A340) was recorded. The rate of decrease in the A340 was directly proportional to the GSH-px activity in the sample, .

2.6.3. Determination of GST Activity

The activity of GST was assayed by using the electrophilic substrate 1-chloro-2,4-dinitrobenzene (CDNB) according to the procedure described by Moron et al. [24]. GST was estimated in 1 mL of incubation mixture containing 905 μL of 0.1 M phosphate buffer (pH 6.5), 20 μL of 20 mM CDNB reagent, 25 μL of 200 mM of reduced GSH, and 25 μL of Triton X100 (0.66%) and preincubated at 37°C for 5 minutes. The reaction was started by adding 25 μL of the liver homogenate. The activity of GST was determined by continuously monitoring the change in absorbance at 340 nm with the spectrophotometer for 3 minutes. The O.D. change/min was calculated, and GST activity was calculated by using the molar extinction coefficient [9.6 mM−1 cm−1] of GST.

2.6.4. Assay of MDA

Malondialdehyde (MDA) was determined according to the method described by Mekheimer et al. and Sayed [25, 26] using 1,1′,3,3′- tetramethoxy propane as standard. In brief, 8.1% SDS was added to the tissue homogenate and incubated for 10 minutes at room temperature, followed by boiling with 20% acetic acid and 0.6% thiobarbituric acid for 60 minutes in a water bath. On cooling, a mixture of pyridine : butanol (1 : 15 v/v) was added and centrifuged at 12000 rpm for 5 min. Absorbance of the upper colored layer was measured at 532 nm and the concentration of MDA was expressed as nmol/mg protein.

2.6.5. Assay of SOD Activity

The activity of SOD was determined as the volume of homogenate that scavenges 50% of the superoxide anion which is generated from the photoillumination of riboflavin in the presence of EDTA (1 unit of SOD activity) [27] using a commercially available kit from BIO-Rad according to the instructions of the manufacturer.

2.6.6. Determination of Nitric Oxide (NO)

The production of NO was determined indirectly by measuring the plasma level of nitrite by a calorimetric method according to Griess reaction [28]. Liver homogenate was diluted four times with water and deproteinized by adding 1/20 volume of ZnSO4 (300 g/L) to a final concentration of 15 g/L. The mixture was centrifuged at 13,000 rpm for 5 min at room temperature. 10 μl of the supernatant was applied to a micro titer followed by 100 μl of Greiss reagent (1% sulfanilamide and 0.1% N-1-naphthyl ethylenediamine dihydrochloride in 2.5% polyphosphoric acid). The absorbance was measured at 540 nm with a Micro Reader (Hyperion, Inc., FL, USA) after 10 min of color development at room temperature. Sodium nitrate solution was used to obtain a standard curve.

2.7. Electrophoretic Mobility Shift Assay (EMSA)

Part of the kidney from different groups was homogenized with 100 μL TOTEX buffer (100 mM HEPES-KOH, pH 7.9, 0.35 M NaCl, 20% glycerol, 1% NP-40, 1 mM MgCl2, 0.5 mM EDTA, 0.5 mM EGTA, 10 μg/mL leupeptin, 0.5 mM DTT, and 0.2 mM PMSF) for 30 seconds and incubated in ice bath for 30 minutes, mixed well, and centrifuged at 13000 rpm for 5 minutes. The supernatant which contained the total nuclear extract of the liver was transferred to a fresh tube and kept at −80°C for EMSA as discussed [29]. The nuclear extract of the liver was assayed for transcription factor binding activity using the NF-κBp65 consensus sequence: 5′-AGTTGAGGGGACTTTCCCAGGC-3′. Specificity of binding was ascertained by competition with a 160-fold molar excess of unlabeled consensus oligonucleotides as previously described [29]. Quantification of activated NF-κB was performed by densitometric analysis of relative EMSA band intensities (R.I.) using ImageJ software using the band of the normal control as a reference band. EMSA experiments were performed at least three times.

2.8. Assay of AGE, TNF-α, and IL-1β

The levels of AGE, TNF-α, and IL-1β were determined using commercially available ELISA kits. The ELISA kits for TNF-α and IL-1β were obtained from R&D (Braunschweig, Germany) while the ELISA kit for AGE was obtained from Roche diagnostics (Mannheim, Germany). All ELISA assays were done according to the manufacturer’s instructions.

2.9. Histopathological Examination

Liver tissues were collected after animal sacrifice, fixed in 10% neutral formalin, and embedded in paraffin. Sections of about 5 μm thick were prepared and stained using H&E as previously described by Fukuzawa et al. [30].

2.10. Statistical Analysis

All group values are expressed as the mean ± SD. Data were evaluated using SPSS 11.09 for Windows. An analysis of variance test was performed initially to test for differences in the treatment, a Tukey post-hoc test was performed to examine whether there were any significant differences between different treatment groups.

3. Results

3.1. Initial and Final Body Weights

The initial and final body weights of all rats in both control and treatment animals were presented in Table 1. There were no differences in the initial body weights of all groups. There was a significant decrease in the body weights of metanil-yellow-treated groups (groups 2–4) when compared to control group. Treatment of the rats with bees’ honey resulted in a significant increase of the final body weight of rats in the groups 5–7.

3.2. Hepatic Biomarkers

As illustrated in Table 1, administration of metanil yellow induced a marked increase in the levels of AST, ALT, ALP, GGT, total bilirubin, and LDH and a significant decrease of serum albumin as compared to the control group. Both effects were found to be dose dependent. Administration of bees’ honey significantly improved some of these hepatic biomarkers and normalized the others as indicated in Table 1.

3.3. Effect on GSH-px

Metanil yellow treatment caused a significant decrease in the level of GSH-px activity in liver tissue when compared with control group (Table 2). The decrease of GSH-px activity in the metanil-yellow-treated groups was dose dependent. The treatment of rats with bees’ honey resulted in a marked increase of GSH-px activity when compared to the metanil-yellow-treated rats ().

3.4. Effect on the Activity of SOD

The activity of SOD in the tissue homogenates of all experimental rats was shown in Table 2. In the liver homogenate, treatment of rats with 50, 100, and 200 mg/kg metanil yellow caused a significant and a dose-dependent reduction of the SOD activity compared to the normal control group. Enhancement of SOD activity was observed as a result of bees’ honey treatment, and the activity was found to be markedly increased.

3.5. Effect on the Activity of GST

Table 2 showed a significant and a dose-dependent decrease in the hepatic GST activity upon metanil yellow treatment as compared to the control group. A significant increase in GST activity was observed in the rat groups treated with bees’ honey as compared to the metanil-yellow-treated groups ().

3.6. Effect on GSH

The effect of bees’ honey on GSH levels for all experimental groups is shown in Table 2. Metanil yellow treatment caused a significant and a dose-dependent decrease of GSH levels in the liver homogenates compared to the normal control group. Rats treated with 50, 100, and 200 mg/kg metanil yellow had a lower GSH content than the normal control group. Administration of bees’ honey significantly modulated these alterations, and the level of GSH rose.

3.7. Effect on Lipid Peroxidation (MDA)

Lipid peroxidation results in the formation of free radicals and induction of oxidative stress. The degree of lipid peroxidation was measured as MDA in rat liver homogenate and the data were shown in Table 2. From the obtained data, it was found that bees’ honey could significantly decrease the formation of malondialdehyde (MDA) in metanil-yellow-treated rats. After 50, 100, and 200 mg/kg metanil yellow administration, the liver MDA level significantly increased. However, the oral administration of bees’ honey resulted in decreasing the level of MDA.

3.8. Effect on Catalase Activity

As a result of metanil yellow administration, the activity of catalase was markedly and dose-dependently reduced. Data in Table 2 showed that the activity of catalase was reduced in the metanil-yellow-treated groups. The orally administrated bees’ honey increased these reduced activities.

3.9. Effect of Bees’ Honey on AGE Levels and Activation of NF-κB

As a result of administration of metanil yellow, the levels of AGE were significantly increased indicating a high degree of oxidative stress and protein glycosylation. Bees honey feeding results in decreasing the elevated AGE as indicated in Table 2. Cumulative studies showed that the overproduction of AGE is a direct cause for the activation of the nuclear factor kaba B (NF-κB) [31, 32].

To test the effect of bees honey on the activation of NF-κB-p65 on the metanil-yellow-treated rats, the EMSA analysis was done. Data of Figures 1(a) and 1(b) showed that the administration of metanil yellow resulted in a significant and dose-dependent NF-κB-p65 activation, reaching a maximum at metanil yellow concentration of 200 mg/kg () compared with the normal control rats. Administration of bees’ honey resulted in a significant reduction of this activated NF-κB-p65.

Figure 1: Binding activity of NF-κB-p65 (a). Group 1, untreated (normal control); groups 2–4, rats treated with 50, 100, 200 mg/kg metanil yellow, respectively; and groups 5–7, rats were treated with metanil yellow as in groups 2–4 plus bees’ honey 2.5 mg·kg−1d−1 for 8 weeks. Binding activity of NF-κB-p65 to its consensus sequence was assayed by EMSA of total protein extracts. Quantification of activated NF-κB-p65 was performed by densitometric analysis of relative EMSA band intensities (b) using the normal control band as a reference band. All values expressed as mean ± S.D. of triplicate tests (). versus group1, versus group 2, versus group 3, versus group 4.

3.10. Effect on NO, TNF-α, and IL-1β

The effect of metanil yellow as well as the effect of bees’ honey on the levels of NO, TNF-α, and IL-1β in rats was studied. Data in Figure 2 showed that the level of NO was markedly and dose-dependently increased as a result of metanil yellow treatment. Administration of bees’ honey reversed these effects and significantly reduced the elevated levels of NO in the groups 5–7 as shown in Figure 2.

In parallel, the levels of TNF-α and IL-1β were significantly and dose-dependently elevated in the metanil-yellow-treated rats (groups 2–4) as indicated in Figures 3 and 4. These elevated levels of TNF-α and IL-1β were significantly reduced as a result of bees’ honey administration.

4. Discussion

Hepatic cells contain high concentrations of hepatic enzymes in the cytoplasm, and AST particularly exists in the mitochondria. Due to the damage caused to hepatic cells, the leakage of cytosol increases the levels of these hepatospecific enzymes in the serum. The elevated serum enzyme levels such as AST and ALT are indicative of cellular leakage and functional integrity of cell membrane in the liver [31]. The measurement of serum AST and ALT levels serves as a mean for the indirect assessment of the condition of the liver. In the present study, the capability of bees’ honey in controlling metanil-yellow-induced hepatotoxicity was observed in that bees honey treated animals had decreased levels of hepatic enzyme in the serum when compared with the metanil yellow groups.

In the present study, we postulated that the hepatoprotective effect of bees’ honey could be attributed to its antioxidant properties. We assayed MDA, a product of lipid peroxidation. MDA was increased in rat liver by induction of hepatotoxicity. However, we showed that bees’ honey significantly reduced MDA formation. Hepatotoxicity not only initiates lipid peroxidation but also reduces tissue GSH-Px, GST, CAT, and SOD activities, and this depletion may result from oxidative modification of these proteins and our data are in line with previous data of Augustyniak et al. [32–34]. Normal cells have a number of mechanisms to defend themselves against the toxic effect of reactive oxygen species (ROS) and oxidative stress including free radical scavengers and chain reaction terminators such as SOD, CAT, and GSH-px systems. SOD removes superoxide radicals by converting them into hydrogen peroxide which is converted by CAT and GSH-px into water. Cellular injury arises when ROS production exceeds the cellular capacity of removal [35–37].

As a result of the increased levels of MDA and the reduced activities of the antioxidant enzymes, the metanil-yellow-treated rats undergo oxidative stress. The induced oxidative stress results in the overproduction of AGE seen in the metanil-yellow-treated rats. AGE combined with their receptors on the cell membrane leading to the activation of NF-κB and its controlled genes. Our data confirmed this hypothesis and are in line with previous studies [29, 31–34, 37]. The anti-inflammatory efficacy of bees’ honey was confirmed by the data obtained from EMSA that showed that bees’ honey feeding resulted in a significant reduction of NF-κB. This is a novel finding that correlates the beneficial effects of bees’ honey with its effect on NF-κB.

In addition, the anti-inflammatory activity of bees’ honey was evaluated in vivo by measuring the release of some inflammatory markers that are controlled by NF-κB like IL-1β, NO, and TNF-α. TNF-α is a proinflammatory cytokine that is elevated in acute and chronic diseases. Some phytochemicals have been shown to inhibit inflammation by blocking inflammatory pathways downstream of cytokine release and also by reducing macrophage production of proinflammatory factors [38]. TNF-α has been reported to play a key role in the pathogenesis of various liver diseases. Following its release from activated Kupffer cells, TNF-α worsens both oxidative stress and inflammatory responses in the liver [39]. In addition, TNF-α stimulates the release of cytokines from macrophages and induces phagocyte oxidative metabolism and NO production. Although several studies have showed that NO protects against liver injury using an NOS inhibitor, certain evidence indicates that excessive NO production by iNOS can lead to hepatic injury [40]. Recent reports also demonstrated that iNOS over reduction occurs in the liver of rats with acute liver injury, which suggested that iNOS may act as a mediator in the pathogenesis of hepatotoxicity in rats [41]. The obtained data are in line with previous work of many research groups [38–43] and are confirmed with the histopathological data in Figure 5.

These results have provided the evidence for the pharmacological effect of bees’ honey in metanil-yellow-induced hepatotoxicity. Overall, bees’ honey not only provided maximum conjugation with injurious free radicals and diminished their toxic properties, but also suppressed the inflammatory responses in metanil-yellow-induced liver injuries. The possible mechanism could be suggested that bees’ honey is able to protect the liver against cellular oxidative damage and maintain of intracellular level of antioxidant enzymes which reduce the overproduction of AGE and attenuate the activation of NF-κB and its controlled genes as well as act as immunomodulator. However, further studies on the active compounds and their biochemical mechanisms responsible for the hepatoprotective effect of bees’ honey will be necessary.

Abbreviations

AGE:

Advanced glycated end products

TNF:

Tumor necrosis factor

IL:

Interleukin.

Acknowledgment

This paper was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, Saudi Arabia, under Grant no. (006-130-D1433). The authors, therefore, acknowledge DSR’ technical and financial support.